Hello,
I know this is off topic, but it came up in this thread. If the mods want to move it I am fine with that.
Often claimed but some perspective is provided by (to my knowledge) the only independent peer reviewed study published in the scientific literature (4 days ago) [1]:
Performance of cartridge and granular carbon dioxide absorbents in a closed-circuit diving rebreather. - PubMed - NCBI
The EAC
is more efficient than a granular canister of the same weight by a margin that varies from 0% to 20% depending on the exercise simulation protocol and CO2 breakthrough end point chosen. Whether 0 - 20% difference represents "quite some margin" is in the eye of the beholder, but it is certainly not the "outlasts a granular system by two times or more" that has previously been claimed.
A 2.6 kg scrubber out-performs a EAC. The average duration of an EAC ventilated at surface pressure in a protocol simulating 6 MET of exercise in our experiments was 158 minutes (EAC in an Optima rebreather), whereas a 2.64 kg scrubber (in an Inspiration EVP) lasted on average 202 minutes.
I'm not entirely sure what Brad means by "minimal caustic cocktail risk" but we found no significant difference in the pH of water eluted from either granular sorb or an EAC after a 5 minute flood (12.7 vs 12.8 respectively).
Possibly under-appreciated because it doesn't exist? We actually found the opposite. On a continuous 6 MET simulated exercise protocol the two scrubbers exhibited almost identical breakthrough kinetics, whereas on a staged exercise protocol (6 MET for half of the expected scrubber life then 2 MET until breakthrough to either 0.5 or 1 kPa inspired CO2) the granular cartridge exhibited a more gradual breakthrough. This was the reason for a duration difference between the two canisters on this protocol where a breakthrough endpoint of 0.5 kPa inspired CO2 was chosen. Because the granular sorb broke through more gradually, it reached 0.5 kPa inspired CO2 more quickly than the EAC whereas the two scrubbers reached 1.0 kPa inspired CO2 at identical times (on average).
Brad will no doubt claim that these results are confounded by the testing of the EAC in a "poorly designed rebreather". Whether this is true or not, and whether the poor design features somehow selectively disadvantage the EAC and not the granular cartridge remain to be seen (I would certainly not take his word for it). But if so, such sensitivity to rebreather design could, of itself, be interpreted as a disadvantage for the EAC. Perhaps more importantly, unlike Deeplife's flagship "iCCR" (deposits taken 10 years ago, still not released) the Optima is a real rebreather being used by real divers. Thus the comparison of its CO2 scrubbing modalities is of real world relevance.
I would like to be clear that neither I nor my team are in any way "anti-EAC". Indeed, it is a very good product, and it works well. What we are "anti" is misleading claims. There have been many claims made around EACs which we wished to investigate, and as a step in this direction we conducted a comparison with granular sorb in a setting that we considered ecologically valid and fair - a rebreather manufactured to take either.
Simon M
Reference:
1. Gant N, van Waart H, Ashworth ET, Mesley P, Mitchell SJ. Performance of cartridge and granular carbon dioxide absorbents in a closed-circuit diving rebreather.
Diving Hyperb Med. 2019;49(4):298-303.